how to stop boiler tube wastage caused by corrosion and
TRANSCRIPT
How to Stop Boiler Tube Wastage Caused by Corrosion and Erosion
WHITEPAPER
Contents
HOW TO STOP BOILER TUBE WASTAGE
CAUSED BY CORROSION AND EROSION
EROSION
CORROSION- GENERAL
CORROSION- REDUCED ATMOSPHERE
FIRESIDE CORROSION
CORROSION AND EROSION CAUSED BY SOOT
BLOWERS (DUAL WASTAGE MECHANISM)
CIRCUMFERENTIAL CRACKING (CORROSION
ASSISTED THERMAL FATIGUE, STRESS
CORROSION CRACKING, QUENCH CRACKING)
CASE STUDIES: ASSET OWNERS EXPERIENCE
WITH HVTS
REFERENCES AND TESTIMONIALS
ABOUT INTEGRATED GLOBAL SERVICES (IGS)
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Boiler tube wastage is a major problem that causes forced outages, unexpected major expense,
affects unit availability, reliability, and ultimately will cost an owner a tremendous amount of
money. There are two maintenance approaches boiler owners will take, proactive and reactive.
Once tubes become too thin, caused by either corrosion or erosion, they need to be replaced.
Extending Tube Life with Added Material
Extending the life of the tube is possible with the use of added material to the OD surface of the
tube, with Inconel Weld Overlay or High Velocity Thermal Spray (HVTS) Cladding. The purpose
of adding material to the tube is to extend its useful life, ultimately preventing panel replacement.
About the White Paper
This paper will discuss HVTS Cladding being used to extend the life of boiler tubes experiencing
severe corrosion and erosion. The HVTS Cladding system can be rapidly installed in-situ or on new
panels and elements.
Figure 1. Scan showing HVTS cladding eliminating corrosion in outlined areas
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How to Stop Boiler Tube Wastage Caused by Corrosion and Erosion
Damage Mechanisms
Erosion can be found in most CFB boilers, sootblower lanes (dual mechanism of corrosion-erosion), and
backpass areas that experience fly ash erosion. The type of corrosion found will depend on the type
of fuel, boiler configuration, and combustion atmosphere. The typical corrosion mechanisms include
fireside corrosion and reduced atmosphere high temperature sulfidation (found mostly in boilers
burning eastern bituminous coal) and circumferential cracking (also known as stress corrosion cracking,
corrosion assisted thermal fatigue, quench cracking).
High Velocity Thermal Spray (HVTS)
• Addresses tube wastage caused by high
temperature sulfidation/ reduced oxygen
atmosphere / Low NOx firing
• Addresses tube wastage caused by erosion – soot
blowers, IK/IR, fly ash
• Delivers long-term reliability by eliminating tube
leaks and disruption to operations
• Is 3x to 5x faster compared to Inconel
weld overlay
• Is 3x to 5x less expensive compared to panel
replacement
• Delivers a 10+ year solution
How to Stop Boiler Tube Wastage Caused by Corrosion and Erosion
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Erosion Resistance
250
200
150
100
50
0
1018 steel
Th
ickn
ess
loss
(mic
ron
)
Stainless Overlay
IGS 8450 (HVTS)
Figure 2. CFB Combustor boiler tubes protected with HVTS Cladding at the tube and refractory interface
ErosionFly ash erosion is the second most important cause for
boiler tube failure (DOE, 1998). Tube erosion in a CFB
combustor can never be stopped, but HVTS Cladding
is proven to slow the wastage down. HVTS Cladding is
20 times more erosion-resistant compared to carbon
steel. Thousands of square feet of surface area can
be rapidly installed during a short outage. The HVTS
Cladding is able to be refurbished during future
outages, thus it is possible to extend boiler tubes’
useful life indefinitely.
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Erosion
Corrosion- GeneralBoiler tube corrosion causes material wastage,
which eventually will lead to equipment failure
due to hoop stress or the replacement of the
material if the mechanism is not identified. The cost
implications are significant. Even if a single tube
failure requires only 24hrs of repair work (usually
not the case), this results in high margin revenue
losses.
The cost of boiler tube failures comprises of three
main components:
1. cost of the repair;
2. cost of startup oil to return unit to service
3. cost of lost production (shut down, repair and
startup time).
The extent and type of corrosion impacting boiler
tubes can vary widely and is driven by a number
of operational conditions. High temperature
corrosion leading to boiler tube wastage does not
follow the rules of wet chemistry and so is often
misunderstood.
Also, mechanisms such as fly ash erosion can
couple with corrosion by removing oxide scales,
thus accelerating wastage rates from boiler tube
corrosion. As another example, some corrosion
phenomena, such as coal ash corrosion, only occurs
at specific temperature ranges.
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Corrosion- General
Figure 3. Zimmer EPRI Study, above
photo as received, below photo after
light sandblasting to reveal HVTS
Cladding has protected the tube from
fireside corrosion (no wall loss)
Corrosion- Reduced Atmosphere Fireside CorrosionIn the past decade, there has been a heavy focus
on reducing environmental emissions. In order
to reduce the production of NOx during the
combustion, low-NOx retrofit burners are used in
the boiler. These burners reduce the production
of NOx by slowing down the combustion, lowering
in this way the temperature of the combustion
and taking the combustion away from the burners
higher up into the furnace.
This is achieved by reducing the amount of oxygen
in the area where the burners are (lower portion
of the furnace) and injecting that oxygen higher up
in the furnace using over-fire air ports. Low-NOx
retrofit causes areas lower in the furnace to be
oxygen starved or under reducing conditions (or in
most severe cases, cycling between both).
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Corrosion- Reduced Atmosphere Fireside Corrosion
Figure 4. Pulverized coal fired boiler experienced slope damage caused by low oxygen levels. HVTS Cladding
was installed to protect the slope tubes from further damage. Photo taken 2 years after HVTS Cladding
application.
Although the whole corrosion process is far
more complex, it can be summarized as follows:
in normal combustion with the presence of
correct amount of oxygen (before low-NOx
burners), the sulfur present in the fuel will
combine with oxygen and remain in gaseous
condition and exit the stack. In a combustion
under reducing conditions (low oxygen), the
sulfur will combine with hydrogen and deposit
on the tube surface reacting with the iron of
the tube material to form a scale of FeS, and
repeat the cycle as more H2S deposits on the
walls, causing significant tube thinning.
HVTS Cladding is ideal for long-term,
reliable protection from the above-described
typical wastage mechanisms. The cladding
composition developed in the mid-2000s
specifically for high temperature sulfidation
environments with the understanding that
permeation and oxide content should be
below critical specified levels for long term
cladding performance.
HVTS Cladding is low-stress, thermal sprayed
metal coating specifically suited for boiler
tube protection in combustion environments
with aggressive sulfidation conditions up to
1800°F (980°C). It is highly protective against
under deposit corrosion, when Sulfur together
with Sodium, Potassium and Vanadium Oxides
form low melting temperature pyro-eutectic
salts.
The high Chromium content, together with
performance enhancing elements provide a
dense stable coating, with high bond strength
due to micro-fusion sites on the substrate. A
thermal expansion coefficient at the midpoint
between carbon and stainless steels makes it
well suited to both as substrate materials. The
material has good erosion resistance due to
effective hard-phase integration.
The HVTS Cladding was also tested by
Electric Power Research Institute (EPRI), in a
1300MW high sulfur coal, supercritical boiler
with Low NOx burner retrofits. Several other
cladding materials were also tested, and the
HVTS Cladding was the only material to fully
protect the substrate from corrosion during
the 39,000 hour testing period.
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Corrosion- Reduced Atmosphere Fireside Corrosion
Oxide Scale
Removed-
Exposed Bare
Tube
Tube Grows
Oxide Layer
Sootblower
Activates
Corrosion and Erosion caused by Soot Blowers (dual wastage mechanism) Plants that operate pulverized coal fired boilers normally use steam or air to clean boiler
tubes. Sootblowers are installed at various boiler locations on the waterwalls, superheaters,
reheaters, and economizers. Wall blowers and IK steam sootblowers (above the nose
arch) cause the most damage. The root cause of the problem is not always 100% erosion.
Corrosion starts the cycle. As the tube builds an oxide scale on the OD of the surface, the
force of the sootblowing activity will remove the scale. After the scale is removed, the tube
will grow more scale, restarting the cycle again.
IK steam stootblowers are notorious for spraying condensate at the start of the cleaning,
which is hard on the nose arch tubes. HVTS Cladding is tough and erosion resistant, but the
material is also very corrosion resistant. The HVTS Cladding will not grow an oxide layer
which will result in no loss caused by the sootblowing process, ending the wastage cycle.
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Corrosion and Erosion caused by Soot Blowers (dual wastage mechanism)
Circumferential Cracking (Corrosion assisted thermal fatigue, stress corrosion cracking, quench cracking)Boiler tube cracking is a major problem for some of the Utilities that operate a boiler that burns
sub-bituminous PRB or lignite coals and also use water cannons. This problem is also seen in
boilers that burn high sulfur bituminous coal, but is less of a problem due to the primary tube loss
being caused by fireside corrosion.
HVTS Cladding will prevent crack growth because it will stop fresh Sulfur from weakening the
tube metal. It is well known the crack growth is a dual mechanism, so by removing one of the root
causes, in this case the corrosion aspect, the crack will stop.
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Circumferential Cracking
Case Studies:Asset Owners Experience with HVTS
RELIABLE BOILER PROTECTION SUPPORTED BY LONG-TERM EPRI STUDY
EPRI STUDY
In the mid 2000s, a US power utility owner and EPRI performed
a long-term study to determine if thermal spray technology
would protect the sidewall tubes (adjacent to burner levels)
from thinning caused by reduced sulfidizing atmospheres. A
test panel with thermal spray products from IGS and another
thermal spray provider were installed. After a 5-year run, the
study concluded the IGS alloy cladding performed well with
no sign of deterioration at all. Other products experienced
cracking and cladding delamination. The important key point
to note is the IGS HVTS alloy cladding protected the tubing
material under the cladding, resulting in zero loss of wall
thickness on the outer surface.Application areas marked out
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Case Studies
PROBLEM
The boiler was experiencing tube wall thickness
wastage caused by operating the boiler in a reducing
atmosphere (low NOx burners) which results in
sulfidation corrosion. This boiler is the newest of the
1300 mw units but experienced very similar corrosion
problems to others in use across the industry. Typical
of boilers retrofitted with low NOx burners, areas of
concern are: Sidewalls adjacent to burner elevations,
front and rear walls in between burners and coutant
slope, convection pass floor wastage caused by coal
ash corrosion, upper furnace corrosion assisted
thermal fatigue (CATF), and economizer wastage
caused by fly ash erosion. IGS HVTS application
Boiler tubes protected
Application sealed with ceramic top-coat
SOLUTION
During the Fall of 2019, the plant was in a major
planned outage. A full furnace scaffold was installed
for boiler maintenance and a tube assessment was
performed. During the inspection, new wastage
was discovered on the upper front wall just below
the wingwalls, near the right sidewall. As a result of
the previous testing of IGS HVTS alloy cladding in
the boiler, and IGS’s status as a long-term, proven
vendor, IGS was contracted to protect the damaged
tubes on a very short notice. The IGS value is more
than just protecting boiler tubes from wastage. IGS
alloy cladding is a permanent solution that is rapidly
installed and improves reliability. Clients who are
proactive in their maintenance strategy can realize
significant capital savings by utilizing the IGS solution
and prevent not only forced outages but eliminate
future tube panel replacements.
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Case Studies
RAPID RESPONSE TO ADDRESS THE BOILER DAMAGE ZONE
SCHEDULED SHUTDOWN
The unit was in a scheduled outage in October 2019, at which
time the fireside of the tubes in the boiler were inspected by
robotic UT. Wastage was discovered on both sidewalls above
the existing field applied overlay, rear wall slope and burners,
and front wall slope and burners. The type of damage is typical
for opposed wall fired pulverized coal boilers operating in a
reducing atmosphere with low NOx burners.
RAPID RESPONSE
IGS was contracted to install 5450 EPRI Proven HVTS Alloy
Cladding over the damage zones. IGS offered a rapid response
and addressed the areas during the week of November 4,
2019. The IGS solution is a rather fast application - a total of
2,000 square foot of boiler tubing was protected with HVTS
in 5 short days.
SAFETY FIRST
The project was executed in accordance with the IGS Safety
Program. Safety is, and always will be Integrated Global
Services’ first and highest priority. Our Management Team
is dedicated to becoming the industry leader in Health and
Safety while our excellent safety record bears witness to
this fact. A continuous improvement process is utilized that
enables all levels of personnel to take part in identifying
and fixing hazards associated within the workplace. This is
marked by our Safety Committee that involves members of
all areas and levels of IGS.
QUALITY
IGS Thermal Spray projects are performed in accordance with
the IGS quality control standards which have been developed
in to meet customer requirements. All site work will be
executed in accordance to the accepted Quality Control Plan
(ITP/QCP) and accompanying method statement. The final
project QC package will be issued along with this report.
Application areas marked out
HVTS application
Completed application
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Case Studies
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“References and
Testimonials
We went from a varied scope and high man hours to lower man hours and
a known scope, which is great for planning for an outage, especially for
the budget. Because of our process and work with IGS we didn’t need to
replace pressure parts. When you start doing pressure part replacement
in circulating fluidized bed boilers, you run into all kinds of issues because
you have to do tube alignment. If the tube alignment is not done correctly,
you’re going to end up with erosion or gouging issues for the rest of the
life of those pressure parts, that’s extremely difficult to fix.
Joel Taylor, Boiler Engineering and Maintenance Specialist. Joel has ensured reliable
operation of 7 Circulating Fluidized Bed Boilers between 4 Plants across his 15 Years of
CFB Experience.
IGS brings to table the technical expertise, the understanding of the boilers, the
technical knowledge behind what the people in the field are doing and you’re
seeing the results. IGS spends a fair amount of time making sure that they’ve got
a good base material and they actually quantify the finish and document that
to ensure a sound product, a sound solution and a sound application. Cladding
thickness measurements give you the ability to determine your wear rates and
what millage you want to apply and need to maintain to be able to get you from
one outage to the next.
Pete Kline, Plant Manager with 28 years CFB Experience, beginning with the initial utilization of
CFB boiler Technology.
References are available on request and can be obtained by getting in touch
with your local IGS representative or emailing [email protected].
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References and Testimonials
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About Integrated Global Services
(IGS)Integrated Global Services (IGS) is the industry leader in the
development and in-situ application of High-Velocity Thermal
Spray (HVTS). The Company has over 30 years of experience
helping customers solve metal wastage problems in mission critical
equipment.
IGS designs solutions that increase plant capacity, increase
equipment availability, and reduce unplanned downtime. Customer
references are extensive and include facilities operated by the
world’s largest energy companies in over 30 countries on 5
continents.
IGS’ HVTS is applied on-site to address problems associated with
erosion and corrosion in many types of boilers utilizing a wide
variety of fuels.
www.integratedglobal.com
About IGS